In production of blow molded articles or containers with threaded neck portions, for example, of the type disclosed in U.S. Pat. No. 4,497,624 which issued to the assignee of the present invention, it is sometimes desirable to mold the parisons or preforms in one injection molding press and at a later time reheat the preforms for blow molding into the substantially larger containers.
It is also well known that the cycle for injection molding preforms is substantially longer than the cycle for blow molding the preforms into larger containers. Thus when producing blow molded containers in high volume, such as the one liter or two liter containers used for carbonated beverages, it has not been practical to blow mold the preforms into containers before the preforms cool and during the injection molding cycle for the preforms.
One type of machine which injection molds preforms and immediately thereafter blow molds the preforms into larger containers is disclosed in U.S. patents issued to Katasi Aoki, including U.S. Pat. No. 4,457,689 and U.S. Pat. No. 32,129. In these blow molding machines, the preforms are transferred from the injection molding station to the blow molding station by means of a rotary indexing disk so that the cycle time for the blow molding operation is the same as the cycle time for the injection molding operation.
Another type of blow molding machine where preforms are blow molded immediately after the preforms are injection molded, is disclosed in U.S. patents issued to Emery I. Valyi, Leonard B. Ryder and Paul Marcus. These patents include U.S. Pat. Nos. 4,405,556, 4,472,131 and 4,376,090. In the blow molding machines disclosed in these patents, the preforms are transferred along a linear path from the preform injection molds to the blow molds, for example, by laterally shifting the core elements for forming the preforms and for blow molding the preforms into larger containers. It is also known to transfer the injection molded preforms from the injection mold immediately after the preforms are molded by means of some form of robotic or other transfer system which also cools the preforms as they are being removed from the injection mold. Such systems are disclosed, for example, in U.S. Pat. Nos. 4,140,464, 4,209,290 and 4,721,452.
When the preforms are produced within an injection mold mounted on a conventional injection molding press which is not equipped with a transfer system, the cycle time for molding the preforms and for allowing the preforms to cool sufficiently within the press, it is usually between twenty to thirty seconds per cycle. This cycle time results from the relatively heavy wall thickness of the preform and the time required to cool the plastics material within the mold from approximately 550 degrees F. down to 150 degrees F. where the preforms may be ejected or stripped from the mold without being deformed or damaged. In order to obtain high volume production of preforms for subsequent blow molding into large containers, it is desirable for the injection mold to have a substantial number of cavities and to minimize the time for molding and cooling the preforms within the injection mold.